The invention relates to the retreading of worn tire carcasses.
More particularly the invention relates to methods for retreading worn tires, of the type wherein a strip of vulcanized tread material is wrapped around a carcass and bonded to the outer periphery of the carcass by means of an intermediate bonding layer.
It is already known to wrap a vulcanized tread strip around the outer periphery of a tire carcass, with a layer of bonding material sandwiched between the carcass and the tread strip. In one such method the carcass, bonding material, and new tread material are wrapped tightly in a casing, and any air trapped between the elements is forced out by means of a strong vacuum. The tightly wrapped carcass, bonding material and new tread material are then heated in an autoclave to the vulcanization temperature of the bonding layer, to effect a permanent bonding of the new tread material to the old carcass.
Another method is known for eliminating air or other gaseous substances from between the old carcass and the new tread material. In that method a circumferentially complete ring of new tread material is stretched to enlarge its circumference and is located concentric to the tire carcass in a sealed chamber. The air is evacuated from the chamber and, in such a vacuum, the stretched ring of tread material is released and permitted to contract upon the carcass. Thereafter, the tread material and carcass are bonded by the conventional vulcanizing method.
Whereas these known methods do accomplish, more or less successfully, the evacuation of air and other gases from between the carcass and new tread material, they leave much to be desired in terms of convenience and simplicity. It is particularly disagreeable to retread tires when each and every tire must be enclosed in a sealed jacket from which the air is then evacuated. These processing steps are cumbersome as such and must in addition be very carefully performed, inasmuch as the presence of air between the carcass and the new tread material very detrimentally effects the resulting bond and the effectiveness and safety of the retreaded tire.